1. Field of the Invention
The present invention relates to an image sensor employed for portable image inputting devices or the like.
2. Description of the Related Art
FIG. 26 is a block diagram showing a main part of a conventional image sensor such as disclosed in Japanese Patent Application Laid-Open No. 8-204899. As illustrated in FIG. 26, a glass plate 2 is fixed to a frame 1 for positioning each of the components, and is also located at the feeding plane of the sheet to be read or original copy 3. An LED substrate 4 is positioned at an angle to the glass plate 2 and fixed to the frame 1. On the LED substrate 4 are arranged linearly a plurality of photo diodes 5 serving as point light emitting elements and these photo diodes 5 constitute a line light source.
On a sensor substrate 6 that is positioned and fixed to the frame 1, a plurality of sensor ICs (integrated circuits) 7 are arranged linearly so as to correspond with the read width of the image sensor. Each of the sensor ICs 7 are several millimeters in length. A rod lens array 8 for forming an orthographic full size image (or a full-scale erect image) is provided between the glass plate 2 and the sensor IC 7. The glass plate 2, the LED substrate 4, the sensor substrate 6, and the rod lens array 8 are fixed to the frame 1 by an adhesive.
Next, the operations will now be explained. A light emitted from the photo diodes 5 is illuminated through the glass plate 2 to the original copy 3. The light illuminated on the original copy 3 is reflected back in accordance with the degree of image contrast on the original copy 3. The reflected light is then transmitted through a rod lenses of the rod lens array 8 to form an image on the sensor IC 7. In the sensor IC 7, electric charges are accumulated depending upon the intensity of the reflected light to output information on the intensity of the reflected light through the sensor substrate 6. Accordingly, the image information of the entire original copy 3 is output by feeding the original copy 3 onto the glass plate 2.
Such a conventional image sensor was mainly employed for image input devices such as facsimiles in which the original copy moves to allow the image to be read in. With the recent popularity of personal computers along with advances in the personalization of various computer peripherals, downsizing image input units is sought.
On the other hand, when conventional image sensors are reduced in size in an attempt to utilize them in a handy scanner, the following problems occur. That is, in the conventional image sensor, the glass plate 2 directly contacts the original copy 3, so the glass plate 2 can be easily damaged by undue force applied by the user, being dropped from a desk, etc. Further, the rod lens array 8 is also reduced in size (e.g., 1 mm (width).times.2-4 mm (height)). Accordingly, when the operating environment temperature varies after the rod lens array 8 is adhered to the frame 1, the rod lens array 8 will be warped because the rod lens array 8 and the frame 1 have different thermal expansion coefficients. As a result, there is a fear that the reflected light emitted from the original copy 3 will not form a image on the sensor IC 7. There is also the fear that proper image formation cannot be obtained because when the glass plate 2 is adhered to the rod lens array 8, they are both dimensioned so small that adhesive flows out onto the surface of the lens at both ends of the rod lens array 8.